In an electrophotographic image forming apparatus, the surface of a photoconductor (image carrier) is uniformly charged by a charger and exposed by a exposing device, so as to form an electrostatic latent image. The electrostatic latent image is then developed by a developing device to form a toner image (developer image), which is then transferred onto such as a paper sheet. In this configuration, the surface of the photoconductor becomes deteriorated by gradual wear-out or by adhesion of foreign matter, causing deterioration of the image quality. To deal with this, technologies for detecting a deteriorated state of the surface of a photoconductor have been developed.
One such technology, a plurality of toner adhesion patterns formed on the surface of a photoconductor in different image forming conditions, and in each of these patterns, the optical density value of a toner-adhered part as well as the background part are measured in order to calculate the ratio therebetween. After that, when the gap of the above ratio is greater than a prescribed value due to the difference of the image forming condition in each of the patterns, the deterioration of the surface of the photoconductor is determined, and an user is informed thereof so that the replacement of the photoconductor is encouraged.
However, in the above technology, a large amount of toner is consumed for detecting a deteriorated state, since a plurality of toner adhesion patterns are formed on the surface of a photoconductor. In the view of the above described circumstance, there is need for a technology that enables both the detection of deterioration of an image carrier and the reduction of the developer consumption.